I have figured out how to add custom information to customers no problem, what i need is custom information specific to each subscription that customer has eg:

Frank Black  - customer

Subscription 1 has 1949 id for the android box they use

Subscription 2 has a 1950 id for a 2nd android box they use.

When they contact us they give us the number 1949 or 1950 so we know what box and subscription they are calling about.

How do we associate this to the subscription? 

So in a nutshell each subscription needs a custom number eg 1949 or 1950 etc, so we know what subscription they are contacting us about.

Thanks for your help in advance!